A cardiac arrhythmia is a condition in which the heart's normal rhythm is disrupted. There are many types of cardiac arrhythmias, including supraventricular arrhythmias that begin above the ventricles (such as premature atrial contractions, atrial flutter, accessory pathway tachycardias, atrial fibrillation, and AV nodal reentrant tachycardia), ventricular arrhythmias that begin in the lower chambers of the heart (such as premature ventricular contractions, ventricular tachycardia, ventricular fibrillation, and long QT syndrome), and bradyarrhythmias that involve slow heart rhythms and may arise from disease in the heart's conduction system.
Catheter ablation is commonly used to treat a variety of cardiovascular conditions, such as cardiac arrhythmias, atrial fibrillation, and other irregularities in the transmission of electrical impulses through the heart. This minimally invasive surgical technique may involve the use of tip electrodes, electrode arrays, cryoballoons, and/or other ablating elements to create lesions or other anatomical effects that disrupt or block electrical pathways through the targeted tissue.
The success of this procedure depends largely on the quality of the lesion(s) created during the procedure. In theory, the most accurate way to assess lesion formation is by monitoring the temperature of the tissue being ablated. However, measuring the temperature of treated tissue during a procedure may be difficult or impossible using known devices and methods, and integrating temperature sensors into the ablation device can increase the size, complexity, and cost of the device. Further, methods that measure temperature within the cryoballoon to approximate the temperature of treated tissue may not take into account the tissue type and response to treatment, and can be very inaccurate. Likewise, temperature-time assessment methods may be based on a one-size-fits-all model that does not take into account the type and depth of tissue, and may be subject to noise in the temperature data.
Further, in the treatment of cardiac arrhythmias, a specific area of cardiac tissue having aberrant electrical activity (e.g. focal trigger, slow conduction, excessively rapid repolarization, fractionated electrogram, etc.) is typically identified first before subsequent treatment. This process, sometimes referred to as localization or mapping, can include obtaining unipolar or bipolar electrograms, or monophasic action potential (“MAP”) electrograms of a particular cardiac region. MAP signals may be obtained by temporarily depolarizing selected tissue, which responsive electrical activity being recorded or otherwise monitored for an indication of local depolarization timing, refractory period duration, and any aberrant electrical activity. After mapping and diagnosing aberrant tissue, a physician may decide to treat the patient by ablating the tissue. Accurate mapping of the cardiac tissue using bipolar, unipolar, or MAP electrogram signals can reduce the number of ablations necessary to treat an aberrant electrical pathway, and can make the executed ablations more effective. Additionally, MAP recordings can substantially improve the ability to determine the timing of local tissue activation, which is often ambiguous when recorded using standard intracardiac electrodes.
Presently, this procedure may require mapping an area of tissue with a first mapping device. Once an optimal ablation site is identified, the mapping device is withdrawn and replaced with an ablation device. However, this practice may increase the chances of patient injury or procedure complications, and may disadvantageously increase the total time needed to treat a condition. Alternatively, presently known devices may include mapping and ablation functionality in a single device, which may reduce procedure time and complexity by eliminating the need to employ separate mapping and ablation devices for each task. Combination mapping and ablation devices also increase ablation accuracy, because once aberrant tissue (the “target tissue”) is found, ablation can begin immediately without having to remove the mapping device and relocating the target tissue with the ablation device. However, such devices may require complicated manufacturing steps and expensive materials, may present insulation problems between mapping and ablation electrodes, and the devices themselves may be prohibitively expensive for some surgeons.
Therefore, it is desirable to provide a cryoablation system, device, and method that allows for accurate temperature-based lesion formation assessment and mapping functionality using a relatively inexpensive catheter accessory that may be used on any aftermarket, over-the-wire balloon catheter.